Rotational actuators

ABSTRACT

An actuator includes a drum defining a longitudinal axis and having axially opposed first and second end portions that are rotatable relative to one another about the longitudinal axis. A shape memory element is wrapped around the drum and extends from the first end portion of the drum to the second end portion of the drum to actuate relative rotation of the first and second end portions of the drum about the longitudinal axis by activation of the shape memory element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to actuation, and more particularly torotational actuation, for example to turn a shaft about its axis.

2. Description of Related Art

A variety of devices are known for actuation. For example, servos,stepper motors, hydraulic or pneumatic pistons, and associated linkagesand gears can be used to provide actuation for rotating, pivoting,sliding, and the like. A typical servo, for example, includes a motor, agear reduction system, and sensors with associated circuitry forfeedback control of the motor.

As there is pressure to make products smaller and less expensive, thereis an ever present desire to make actuators more simple, compact, and atlower cost. The aerospace industry is one example where size, cost, andcomplexity are very important. One exemplary actuator, disclosed in U.S.Pat. No. 4,761,955 to Bloch, which is incorporated herein by referencein its entirety, uses a shape memory alloy wire wound through six setsof pulleys of a rotary accumulator as the basis for an actuator.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for actuators that allow for improved simplicity, size, cost,and the like. There also remains a need in the art for such actuatorsthat are easy to make and use. The present invention provides a solutionfor these problems.

SUMMARY OF THE INVENTION

A new and useful actuator includes a drum defining a longitudinal axisand having axially opposed first and second end portions, e.g., groundedand actuated end portions, respectively, that are rotatable relative toone another about the longitudinal axis. A shape memory element iswrapped around the drum and extends from the first end portion of thedrum to the second end portion of the drum to actuate relative rotationof the first and second end portions of the drum about the longitudinalaxis by activation of the shape memory element.

The drum can be configured and adapted to provide proportionally greatertravel in a direction along the longitudinal axis for the shape memoryelement as the shape memory element is actuated around the drum. Forexample, in certain embodiments, the first and second end portions ofthe drum can be connected to one another by a torsionally flexible drumportion. The flexible drum portion can include a composite material thatprovides for a torsionally compliant, radially rigid drum portion. Thetorsional flexibility of the drum can be chosen by material selectionand by the presence of cutouts or slots in the drum. The flexible drumportion is annular with slots as required defined therethrough, whereinthe slots are aligned in a generally axial direction to lower thetorsional rigidity of the drum. Each slot is defined between respectiveaxial strips of the annular flexible drum portion. The strips areconfigured and adapted to flex progressively in the angular (torsion)direction between the first and second end portions of the drum underforce of the shape memory element when activated and to resiliently biasagainst the shape memory element to return the drum to a relaxed statewhen the shape memory element is deactivated. The drum can include astop to provide bias torque in the drum for reverse actuation of thedrum with the shape memory element deactivated. The strips canadvantageously be stiff in the radial direction to resist theconstricting force of the wound shape memory element.

In accordance with certain embodiments, the drum includes a plurality ofdiscs axially stacked, wherein each disc is free to rotate independentlyaround the longitudinal axis. A torsion spring can operatively connectthe first and second end portions of the drum to bias against the shapememory element to return the drum to an original condition upondeactivation of the shape memory element.

It is also contemplated that the drum can include a plurality of taperedrollers circumferentially spaced apart about the longitudinal axis,wherein each tapered roller has an reduced diameter end proximate thefirst end portion of the drum and an opposed enlarged diameter endproximate the second end portion of the drum. The shape memory elementcan define a polygonal path winding around the tapered rollers. Thesecond end portion of the drum can include a splined output flange, orany attachment arrangement suitable for the transmission of therotational torque and motion.

These and other features of the systems and methods of the subjectinvention will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art will readily understand how to make anduse the devices and methods of the subject disclosure without undueexperimentation, preferred embodiments thereof will be described indetail herein below with reference to certain figures, wherein:

FIG. 1 is a schematic perspective view of an exemplary embodiment of anactuator, showing the shape memory element wrapping around the flexibleannular drum portion;

FIG. 2 is a schematic perspective view of another exemplary embodimentof an actuator, showing a drum that includes a stack of rotating discs;

FIG. 3 is a schematic perspective view of another exemplary embodimentof an actuator, showing a drum with tapered rollers; and

FIG. 4 is a schematic end view of the actuator of FIG. 3, showing thepolygonal wrapping of the shape memory element about the taperedrollers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectinvention. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of an actuator inis shown in FIG. 1 and is designated generally by reference character100. Other embodiments of actuators, or aspects thereof, are provided inFIGS. 2-4, as will be described. The systems described herein can beused to provide rotational actuation, for example oscillatory actuationabout the axis of a shaft.

Actuator 100 includes a drum 102 defining a longitudinal axis A andhaving a first end portion 104 axially opposed to a second end portion106. End portions 104 and 106 are rotatable relative to one anotherabout the longitudinal axis A. A shape memory element 108 is wrappedaround drum 102 and extends from first end portion 104 to second endportion 106. This allows element 108 to actuate or drive relativerotation of the first and second end portions 104 and 106 aboutlongitudinal axis A by activation of the shape memory element 108.Element 108 can be of any suitable shape memory alloy or material suchas Nitinol, and can be activated, for example by applying a voltageacross its respective ends to provide heat for the shape memory effectshortening element 108.

With continued reference to FIG. 1, first and second end portions 104and 106 are connected to one another by a flexible annular drum portion110. In this embodiment, portion 110 has slots defined therethrough,wherein the slots are aligned in a generally axial direction. Someobliqueness in the slots relative to the axial direction may bedesirable in the relaxed state for certain applications to counteractaxial shortening of the drum that can occur during actuation. Each slotis defined between respective axial strips 112 of portion 110. Thestrips 112 are configured and adapted to flex progressively between thefirst and second end portions 104 and 106 under force of the shapememory element 108 when activated. In their flexed state, strips 112resiliently bias against the shape memory element 108, and can returntoward a relaxed state when the shape memory element 108 deactivated.The strips 112 are configured to provide a sufficient return torque torestretch element 108 and provide any extra torque needed to provideactuation torque in the return direction. Some remaining bias can beexpected to match the yield strength of the element 108. Even more biascan be included so there is useable torque available at the (return) endof travel—in this case the actuator could include a rotation stop, sothis remaining torsional bias does not continue to stretch element 108beyond its design limits. Thus activating and deactivating element 108,e.g., by switching an electrical current through element 108 on and off,can actuate drum 102 back and forth around axis A. End portion 106includes a splined output flange 114.

The actuation of the element 108 shortens the wrapped element 108 andwould simply constrict or radial squeeze the drum, however if the drumis sufficiently rigid to resist this radial squeezing, then thesecondary effect is an induced twisting of the second end of the drumrelative to the first end. The twisting effect is the intended anddesirable result of this configuration. Drum 100 can be made of acomposite material that provides for a torsionally complaint, radiallyrigid drum portion. It should be noted that the tangential location ofany portion of element 108 moves progressively more the farther it isfrom the grounded end of the actuator drum. The embodiments describedherein afford a means for the progressively greater tangential motion ofthe shape memory element along the length and circumference of the drum.

Drum 100 is configured and adapted to provide proportionally greatertravel in a direction along the longitudinal axis for element 108 aselement 108 is actuated around drum 100, e.g., to reduce relative motionlocally between drum 100 and element 108. This can also be accomplishedin other ways. For example, with reference now to FIG. 2, actuator 200includes a drum 202 that includes a plurality of discs 210 that areaxially stacked. Each disc 210 is free to rotate independently aroundthe longitudinal axis A. This relative rotation can be accomplished byconnecting each disc 210 to shaft 214 with a respective bearing,bushing, or the like. A shape memory element 208, similar to element 108described above, wraps around drum 202 to actuate relative rotation ofthe first and second end portions of drum 202.

With reference now to FIGS. 3-4, actuator 300 has a drum 302 thatincludes a plurality of tapered rollers 310 circumferentially spacedapart about the longitudinal axis A. Each tapered roller 310 has itsreduced diameter end proximate the first end portion 304 of drum 302 andits opposed enlarged diameter end proximate second end portion 306.Shape memory element 308 defines a polygonal path winding around taperedrollers 310, as shown in FIG. 4. A torsion spring 316 is mounted insidedrum 302, as indicated schematically in FIG. 3, to connect the first andsecond end portions of drum 302 to bias against element 308 to returndrum 302 to its original condition upon deactivation of element 308,much as described above with respect to the resilient strips 110 inFIG. 1. One end portion 306 rotates relative to the rest of drum 302,and element 308 and spring 316 are mounted to rotate end portion 306relative to the rest of drum 302.

The exemplary actuator embodiments described above all include means foraccommodating progressive movement of the shape memory element along therespective drum. For example, if a shape memory element such as Nitinolis used, it can be pre-stretched. When activated by applying a voltageacross the element, it will shrink by about 10% in length. If one end ofthe drum is held stationary, the opposite end will experience fullmotion, but the intermediate portions of the drum will undergopropositionally less motion, to match the motion of the shape memoryelement as it grows and shrinks. This reduces friction or bindingbetween the surface of the drum and the shape memory element.

FIG. 1 shows element 108 having four coils around drum 102. Thoseskilled in the art will readily appreciate that this is only exemplary.Greater numbers of coils in the shape memory element will result ingreater angular movement of the actuator. So actuators can be designedfor specific applications with any suitable number of coils to achievethe desired angular travel.

While shown and described in the exemplary context of having the shapememory element wrapped around the outside of the drum, those skilled inthe art will readily appreciate that the shape memory element canreadily be wrapped around within the drum or inside of the drum, ifsuitably retained, without departing from the scope of this disclosure.Additionally, while shown and described in the exemplary context ofhaving a single wire, constant diameter type shape memory element, thoseskilled in the art will readily appreciate that multiple shape memoryelements, multi-stranded elements, and non-constant cross-sectionalelements can all be tailored to provide a specific torque for a givenapplication without departing from the scope of this disclosure. Theresponse time of the actuators described herein can be increased byenhancing the heat transfer to the shape memory elements.

The methods and systems, as described above and shown in the drawings,provide for actuators with superior properties including for example,simplicity, size, cost, and the like. While the apparatus and methods ofthe subject disclosure have been shown and described with reference topreferred embodiments, those skilled in the art will readily appreciatethat changes and/or modifications may be made thereto without departingfrom the scope of the subject disclosure.

What is claimed is:
 1. An actuator comprising: a drum defining alongitudinal axis and having axially opposed first and second endportions that are rotatable relative to one another about thelongitudinal axis; and a shape memory element wrapped around the drumand extending from the first end portion of the drum to the second endportion of the drum to actuate relative rotation of the first and secondend portions of the drum about the longitudinal axis by activation ofthe shape memory element, wherein the first and second end portions ofthe drum are connected to one another by an annular flexible drumportion with slots defined therethrough, wherein the slots are alignedin an oblique direction relative to the longitudinal axis in a directionopposed to actuator rotation in a relaxed state.
 2. An actuator asrecited in claim 1, wherein each slot is defined between respectiveaxial strips of the annular flexible drum portion, wherein the stripsare configured and adapted to flex progressively between the first andsecond end portions of the drum under force of the shape memory elementwhen activated and to resiliently bias against the shape memory elementto return to a more relaxed state with the shape memory elementdeactivated.
 3. An actuator comprising: a drum defining a longitudinalaxis and having axially opposed first and second end portions that arerotatable relative to one another about the longitudinal axis; and ashape memory element wrapped around the drum and extending from thefirst end portion of the drum to the second end portion of the drum toactuate relative rotation of the first and second end portions of thedrum about the longitudinal axis by activation of the shape memoryelement, wherein the drum includes a plurality of tapered rollerscircumferentially spaced apart about the longitudinal axis, wherein eachtapered roller has a frustoconical cross-section extending from areduced diameter end proximate the first end portion of the drum to anopposed enlarged diameter end proximate the second end portion of thedrum.
 4. An actuator as recited in claim 3, wherein the shape memoryelement defines a polygonal path winding around the tapered rollers. 5.An actuator as recited in claim 1, wherein the second end portionincludes an attachment for transmission of the rotational torque andmotion.
 6. An actuator as recited in claim 1, wherein the second endportion includes a splined output flange.
 7. An actuator as recited inclaim 1, further comprising a torsion spring operatively connecting thefirst and second end portions of the drum to bias against the shapememory element to return the drum to an original condition upondeactivation of the shape memory element.
 8. An actuator as recited inclaim 1, wherein the drum is configured and adapted to provideproportionally greater travel in a direction along the longitudinal axisfor the shape memory element as the shape memory element is actuatedaround the drum.
 9. An actuator as recited in claim 1, wherein theflexible drum portion includes a composite material that provides for atorsionally compliant, radially rigid drum portion.
 10. An actuatorcomprising: a drum defining a longitudinal axis and having axiallyopposed first and second end portions that are rotatable relative to oneanother about the longitudinal axis; and a shape memory element wrappedaround the drum and extending from the first end portion of the drum tothe second end portion of the drum to actuate relative rotation of thefirst and second end portions of the drum about the longitudinal axis byactivation of the shape memory element, wherein the first and second endportions of the drum are connected to one another by an annular flexibledrum portion with slots defined therethrough, wherein each slot isdefined between respective axial strips of the annular flexible drumportion, wherein the strips are configured and adapted to flexprogressively between the first and second end portions of the drumunder force of the shape memory element when activated and toresiliently bias against the shape memory element to return to a morerelaxed state with the shape memory element deactivated, wherein thedrum includes at least one stop to provide bias torque in the drum forreverse actuation of the drum with the shape memory element deactivated.